AgroBiogen Volume 2 Nomor 1 April 2006_2

JURNAL AgroBiogen
2 Nomor 1 April 2006


Nodulation and Growth of a Supernodulating Soybean Mutant SS2-2
Symbiotically Associated with Bradyrhizobium japonicum

(Puji Lestari 1, Kyujung Van 2, Moon Young Kim 2, and Suk-Ha Lee 2)

1 Indonesian Center for Agricultural Biotechnology and Genetic Resources Research and Development
Jl. Tentara Pelajar No. 3A, Bogor 16111
2 Seoul National University, Seoul, 151-742, Korea


Nodulasi dan Pertumbuhan Mutan Kedelai Penghasil Nodulsuper SS2-2 dalam Asosiasi Simbiotik dengan Bradyrhizobium japonicum. Puji Lestari, Kyujung Van, Moon Young Kim, dan Suk-Ha Lee. Mutan kedelai penghasil nodulsuper menunjukkan kelemahan dalam kontrol autoregulasi pada nodulasi dan perbedaan fenotip dibandingkan dengan tipe liarnya. Studi untuk mengevaluasi karakter pertumbuhan dan nodulasi dari kedelai penghasil nodulsuper dalam asosiasinya dengan Bradyrhizobium japonicum dilakukan dalam penelitian ini. Tiga genotip kedelai, yaitu mutan kedelai penghasil nodulsuper SS2-2, tipe liarnya Sinpaldalkong 2 dan kedelai kontrol Jangyeobkong diinokulasi dengan B. japonicum USDA 110, kemudian ditumbuhkan di rumah kaca dalam kondisi terkontrol. Karakter nodulasi, fiksasi nitrogen (Acetylene Reduction Activity/ARA), pertumbuhan tanaman, dan hasil biji ditentukan untuk mengevaluasi asosiasi simbiotik antara B. japonicum dan kedelai nodulsuper. Kedelai yang diinokulasi dengan B. japonicum menunjukkan peningkatan jumlah dan berat kering nodul serta berat kering total tanaman dibandingkan dengan tanpa inokulasi. Tanaman SS2-2 yang diinokulasi menunjukkan jumlah nodul sekitar 20 kali lipat lebih tinggi daripada tipe liarnya. Inokulasi B. japonicum ternyata juga meningkatkan fiksasi nitrogen seiring dengan perkembangan nodul. Tanaman S2-2 lebih pendek dan menghasilkan fiksasi nitrogen (ARA) lebih tinggi, tetapi spesifik ARA dan hasil biji lebih rendah dibandingkan dengan tipe liarnya. Berdasarkan hasil evaluasi terhadap nodulasi dan pertumbuhannya, interaksi Rhizobium dan kedelai penghasil nodulsuper SS2-2 mempunyai respon asosiasi simbiotik lebih rendah dibandingkan kedelai penghasil nodul normal (kedelai yang tidak mendapat perlakuan mutasi).

Keywords: Bradyrhizobium japonicum, fiksasi nitrogen, fenotip, kedelai nodulsuper.

A symbiosis between the soil bacteria and leguminous plants is characterized by a specific multi step signal exchange (Israel et al. 1986). The nodulation of soybean plants is a developmentally complex process requiring interaction between Bradyrhizobium and the host plants (Sutton 1983). Successful development of nitrogen-fixing nodules, including supernodulating soybean requires ongoing communication between the plant host and the endosymbiotic Rhizobium (Green and Emerich 1999).
In soybean, nodulation mutants have been isolated either from normal soybean population or by chemical or physical mutagenesis (Carroll et al. 1985a; Gremaud and Harper 1989). Three groups of scientists have independently isolated supernodulating or hypernodulating soybean mutants from cultivars Bragg (Carroll et al. 1985a), Williams (Gremaud and Harper 1989), and Enrei (Akao and Kouchi 1992). All these mutants were capable of producing severalfold more nodules than their parent lines in the presence of nitrate. These supernodulating soybean mutants may not only be unique biological materials for a study on host plant factors, which could be involved in the process of nodulation, but also be a useful germplasm in a breeding program on improvement of nodulation and nitrogen fixation (Lee et al. 1997).
The super and hypernodulating soybean mutants formed considerably more nodules than their wild type, and an extensive region of the roots was covered with nodules (Akao and Kouchi 1992). Several soybean mutants generated from cv. Bragg (Carroll et al. 1985a) were described as supernodulators and nitrate tolerant symbiotic (nts) mutants. These mutants displayed N-fixation and produced nodule 10 times more than their wild type (Carroll et al. 1985b). Evaluation of the supernodulating soybean mutants in the field have been reported in previous studies, involving mutants of soybean cultivars Bragg and Williams (Herridge and Rose 1994). It was revealed that intermediate supernodulators could grow as vigorously as their parent cultivars. However, the yield of extreme supernodulators (nts382, nts1007, mutants of Bragg) and intermediate supernodulators (nts1116) have been consistently low (Song et al. 1995). Supernodulating soybean mutants also showed higher activities in the N fertilized than commercial cultivars Bragg, Centaur, and Manark (Song et al. 1995). It has been suggested that these were due to other mutations unrelated to nodulation (Mathews et al. 1989). In series of split-root and grafting experiment, the autoregulatory response was found to be systemic (Ollsson et al. 1989), requiring the action of the shoot (Delves et al. 1986).
The yield of supernodulating mutant SS2-2, generated from Sinpaldalkong 2 that was mutagenized by EMS (Lee et al. 1997), was not changed significantly due to nitrogen supply. Furthermore, noninoculated plants of mutants, SS2-2 and nts382 showed greater nodules number and nodule mass, as well as greater ARA than their wild types, regardless of the level of exogenous nitrogen supply (Ha et al. 1999). Investigation of nitrogen fixation and agronomical traits of SS2-2 in association with Rhizobium has not been reported. This paper therefore, reported a study on a supernodulating soybean SS2-2 that was compared with its wild type in growth and nodulation in response to Bradyrhizobium japonicum.

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